Carbohydrates provide fuel for the tissues of your body, and absorption allows digested carbohydrates to enter your bloodstream so you can use this
Carbohydrates provide fuel for the tissues of your body, and absorption allows digested carbohydrates to enter your bloodstream so you can use this energy. Absorption takes place in the upper portion of your small intestine, a digestive organ that includes small structures called villi and microvilli. These hairlike projections lining the cells in this part of your gut greatly increase the surface area available for carbohydrate absorption.
Digestible dietary carbohydrates are of two general types: sugars and starch. Sugars can be monosaccharides, or single sugars, such as glucose, galactose and fructose, while two single sugars joined together create a disaccharide. For instance, the milk sugar lactose consists of a glucose linked to a galactose. Your digestive system absorbs only monosaccharides, so you must first digest any disaccharides into their single sugars before you can benefit from them. Similarly, starch – composed of many glucose molecules bound together into a large unit – must undergo digestion until only single glucose molecules remain, ready to be absorbed.
Once digestion creates a pool of glucose in your gut, absorptive cells lining your small intestine begin to transport the sugar from your gut to your bloodstream. These cells, called enterocytes, lie as a sort of boundary between your gut and your capillaries, and they absorb glucose with the help of both sodium and a protein-based transporter molecule. The transporter molecule within the enterocyte moves to the cell membrane closest to your gut and first binds sodium, which changes the shape of the transporter so it can now also grab a single glucose molecule from within your gut. The transporter moves to the interior of the cell, where it releases first the sodium and then the glucose. A different transporter grabs the glucose from the interior of the cell and carries it across to the other side of the enterocyte, releasing it into your bloodstream.
Galactose and fructose are typically much less abundant in your diet than glucose, but their absorption takes place in the same area of your gut. In fact, galactose moves into the enterocyte using the same process and transporter molecule as glucose, and therefore it is also dependent upon the presence of sodium. In contrast, fructose travels into the cell with a different type of transporter than that used by glucose and galactose, and the transporter does not require sodium in order to bind the sugar. However, both galactose and fructose move from the inside of the enterocyte to your bloodstream using the same transporter.
Although potassium is not directly involved in the absorption of carbohydrates into your bloodstream, it plays an important role in sodium function and, indirectly, in water absorption. When the transporter releases sugar from the enterocyte into the blood, it also releases sodium. To maintain the correct osmotic pressure within the cell, potassium enters the cell as sodium leaves. As this happens, the concentration difference allows water absorption into your bloodstream along with other nutrients.